In numerous ophthalmological measurements and/or surgical interventions, the constant accommodation of a patient's eye is stabilized by offering the patient a target object (so-called target), typically in the form of a light source. The patient fixates (sights, looks at) this light source without interruption. In the process, the patient will unintentionally attempt to see the target object (target) sharply. However, if the fixating eye has aberrations, the focusing can only occur more or less incompletely.
The known devices for the fixation of an eye according to the prior art take into account an ametropia of the eye only in terms of focusing relative to defocus, that is blurriness, which results from obtaining a sharp representation of a point to be pictured in front of or behind the retina. Such defocus is referred to as a low order aberration. In ophthalmology, the imaging properties of the eyes are usually represented with so-called Zernike polynomials. The defocus relates to the Zernike polynomial Z4 (see FIG. 4). In the prior art, an attempt is made to reduce the defocus during fixation, for example, by shifting the lenses or lens systems and/or by shifting the target object for the purpose of increasing or shortening the object distance.